Experimental studies are designed to elucidate the molecular basis of the primary events in photoreception and transduction in the process of vision. Direct emphasis is given to the structural and functional role played by rhodopsin, the chromophoric protein photoreceptor. Upon absorption of light the chromophore, 11-cis retinal which is embedded in the protein, goes through a sequence of spectrally characterized events in which it is isomerized from 11-cis to the all trans form. Subsequently, there occurs a change in the electrical potential of the cell's membrane, the result of triggering. Sequential chromophoric changes will be related on the same timescale with the dynamic changes in protein structure and in membrane environment in order to "map out" the molecular events rhodopsin experiences in the process of visual transduction. These events which occur in less than 1 millisecond will be studied by rapid kinetic techniques. Flash photolysis spectroscopy will be used to observe the transient changes occurring; the various changes will then be correlated on a common timescale. Experiments will probe features of the chromophore site, features of protein structure and features of the membrane environment required by rhodopsin to function dynamically as a molecular trigger.